Add io.Reader variant

Move core logic to ParseTestCases,
which operates on an io.Reader,
but keep the file-based function around for convenience.

testutil/testutil.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 	"regexp"
 	"runtime/debug"
@@ -99,10 +100,7 @@ func (e *testCaseParseError) Unwrap() error {
 	return e.Err
 }
 
-// ParseTestCaseFile parses the contents of the given test case file
+// ParseTestCases parses test cases from a source in the following format:
-// and reurns the test cases found inside.
-//
-// The file should contain zero or more test cases, each in the form:
 //
 //	NUM[:DESC]
 //	[OPTIONS]
@@ -143,13 +141,7 @@ func (e *testCaseParseError) Unwrap() error {
 //	//- - - - - - - - -//
 //	Hello, **world**.
 //	[..]
-func ParseTestCaseFile(filename string) ([]MarkdownTestCase, error) {
+func ParseTestCases(fp io.Reader) ([]MarkdownTestCase, error) {
-	fp, err := os.Open(filename)
-	if err != nil {
-		return nil, err
-	}
-	defer fp.Close()
-
 	scanner := bufio.NewScanner(fp)
 	c := MarkdownTestCase{
 		No:          -1,
@@ -169,6 +161,7 @@ func ParseTestCaseFile(filename string) ([]MarkdownTestCase, error) {
 		}
 	}
 
+	var err error
 	for scanner.Scan() {
 		line++
 		if util.IsBlank([]byte(scanner.Text())) {
@@ -232,6 +225,18 @@ func ParseTestCaseFile(filename string) ([]MarkdownTestCase, error) {
 	return cases, nil
 }
 
+// ParseTestCaseFile reads test cases as described by [ParseTestCases]
+// from an external file.
+func ParseTestCaseFile(filename string) ([]MarkdownTestCase, error) {
+	fp, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer fp.Close()
+
+	return ParseTestCases(fp)
+}
+
 // DoTestCaseFile runs test cases in a given file.
 func DoTestCaseFile(m goldmark.Markdown, filename string, t TestingT, no ...int) {
 	allCases, err := ParseTestCaseFile(filename)

testutil/testutil_test.go

@@ -3,7 +3,6 @@ package testutil
 import (
 	"errors"
 	"os"
-	"path/filepath"
 	"reflect"
 	"strings"
 	"testing"
@@ -13,7 +12,7 @@ import (
 // that doesn't conform to testing.T.
 var _ TestingT = (*testing.T)(nil)
 
-func TestParseTestCaseFile(t *testing.T) {
+func TestParseTestCases(t *testing.T) {
 	tests := []struct {
 		desc string
 		give string // contents of the test file
@@ -85,12 +84,7 @@ func TestParseTestCaseFile(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.desc, func(t *testing.T) {
-			filename := filepath.Join(t.TempDir(), "give.txt")
+			got, err := ParseTestCases(strings.NewReader(tt.give))
-			if err := os.WriteFile(filename, []byte(tt.give), 0o644); err != nil {
-				t.Fatal(err)
-			}
-
-			got, err := ParseTestCaseFile(filename)
 			if err != nil {
 				t.Fatalf("could not parse: %v", err)
 			}
@@ -104,7 +98,7 @@ func TestParseTestCaseFile(t *testing.T) {
 	}
 }
 
-func TestParseTestCaseFile_Errors(t *testing.T) {
+func TestParseTestCases_Errors(t *testing.T) {
 	tests := []struct {
 		desc   string
 		give   string // contents of the test file
@@ -166,12 +160,7 @@ func TestParseTestCaseFile_Errors(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.desc, func(t *testing.T) {
-			filename := filepath.Join(t.TempDir(), "give.txt")
+			cases, err := ParseTestCases(strings.NewReader(tt.give))
-			if err := os.WriteFile(filename, []byte(tt.give), 0o644); err != nil {
-				t.Fatal(err)
-			}
-
-			cases, err := ParseTestCaseFile(filename)
 			if err == nil {
 				t.Fatalf("expected error, got:\n%#v", cases)
 			}
@@ -185,6 +174,18 @@ func TestParseTestCaseFile_Errors(t *testing.T) {
 	}
 }
 
+func TestParseTestCaseFile_Error(t *testing.T) {
+	cases, err := ParseTestCaseFile("does_not_exist.txt")
+	if err == nil {
+		t.Fatalf("expected error, got:\n%#v", cases)
+	}
+
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Errorf("  unexpected error = %v", err)
+		t.Errorf("expected unwrap to = %v", os.ErrNotExist)
+	}
+}
+
 func TestTestCaseParseError(t *testing.T) {
 	wrapped := errors.New("great sadness")
 	err := &testCaseParseError{Line: 42, Err: wrapped}